(function() {

  var C = (typeof window === 'undefined') ? require('./Crypto').Crypto : window.Crypto;

  // Shortcuts
  var util = C.util,
    charenc = C.charenc,
    UTF8 = charenc.UTF8,
    Binary = charenc.Binary;

  C.HMAC = function(hasher, message, key, options) {

    // Convert to byte arrays
    if (message.constructor == String) message = UTF8.stringToBytes(message);
    if (key.constructor == String) key = UTF8.stringToBytes(key);
    /* else, assume byte arrays already */

    // Allow arbitrary length keys
    if (key.length > hasher._blocksize * 4)
      key = hasher(key, {
        asBytes: true
      });

    // XOR keys with pad constants
    var okey = key.slice(0),
      ikey = key.slice(0);
    for (var i = 0; i < hasher._blocksize * 4; i++) {
      okey[i] ^= 0x5C;
      ikey[i] ^= 0x36;
    }

    var hmacbytes = hasher(okey.concat(hasher(ikey.concat(message), {
      asBytes: true
    })), {
      asBytes: true
    });

    return options && options.asBytes ? hmacbytes :
      options && options.asString ? Binary.bytesToString(hmacbytes) :
      options && options.asBase64 ? util.bytesToBase64(hmacbytes) :
      util.bytesToHex(hmacbytes);

  };

})();